Interlining materials are the invisible framework of clothing. They ensure a correct fit and optimal comfort for the wearer. Depending on the application, they facilitate processability, increase functionality and stabilize the clothing. In addition to clothing, they can also undertake these functions in technical textile applications, such as in the furniture, upholstery and home textiles industry.
Important property profiles for interlining materials are softness, resilience, grip, washing and care resistance and sufficient abrasion resistance of the carrier material in use. Furthermore, it is advantageous if the interlining materials have a good and lasting wash resistance, preferably at high temperatures, and withstand demanding post-processing steps such as drying conditions over a high number of cycles and/or the so-called “frost process”. The frost process is a dyeing process to create an irregular color pattern and is described, for example, in WO 2007/088115 A1. In this method, the textile products to be dyed are dyed together with granules, which are impregnated with an inertizing liquid. The frost process puts a huge strain on the materials being treated.
Interlining materials can consist of nonwovens, wovens, knitted fabrics or comparable textile fabrics, which are usually additionally provided with an adhesive composition, as a result of which the interlining can be bonded to a face material usually thermally by heat and/or pressure (fusible interlining). The interlining is therefore laminated onto a face material. The various fabrics mentioned each have different property profiles depending on the production method. Wovens consist of threads/yarns in the warp and weft directions; knitted fabrics consist of threads/yarns which are connected to make a textile fabric using a stitch construction. Nonwovens consist of individual threads laid to make a fibrous web, which is bonded mechanically, chemically or thermally.
In the case of mechanically bonded nonwovens, the fibrous web is bonded by the mechanical intertwining of the fibers. For this purpose, either a needling technique or intertwining by means of water or steam jets is used. Needling produces soft products. However, mechanical needling is usually dependent on a mass per unit area of >50 g/m2, which is too heavy for a large number of interlining applications. Nonwovens bonded by water jets, however, can be achieved with lower masses per unit area.
In the case of chemically bonded nonwovens, the fibrous web is provided with a binding agent (for example an acrylate binding agent) by impregnation, spraying or by means of other standard application methods, and is then condensed. The binding agent binds the fibers to one another to form a nonwoven.
Thermally bonded nonwovens are usually bonded by calendering or by hot air for use as interlining materials. In the case of interlining nonwovens, point calender bonding prevails nowadays as the standard technology. In the process, the fibrous web normally consists of fibers made from polyester or polyamide specially developed for this process, and is bonded by means of a calender at temperatures around the melting point of the fibers, a roller of the calender being provided with engraved points. Such engraved points consist, for example, of 64 points/cm2 and can, for example, have a welding surface of 12%. Without a point arrangement, the interlining material would be bonded across the whole surface and would be unsuitably hard to the touch.
The different methods described above for producing textile fabrics are known and are described in specialist books and in patent literature. The adhesive compositions which are usually applied to interlining materials can mostly be thermally activated and normally contain thermoplastic polymers. The technology for applying these adhesive composition coatings takes place according to prior art in a separate work step on the fibrous fabric. Powder dot methods, paste printing methods, double dot methods, scatter methods and hot-melt methods are usually known as adhesive composition technology and are described in patent literature. Nowadays, double dot coating is regarded as the most efficient as regards adhesion to the face material even after care treatment and with respect to the back of the material sticking to the machine.
Such a double dot has a two-layered structure. It consists of a lower dot and an upper dot. The lower dot penetrates the base material and acts as a barrier layer against adhesive composition return and as an anchor for the upper dot particles. Standard lower dots consist, for example, of binding agents and/or a thermoplastic polymer, which contributes to the adhesive strength during fusion. Depending on the chemicals used, the lower dot contributes as a barrier layer to the prevention of adhesive composition return in addition to anchoring in the base material. The principal adhesive component in the two-layered compound is primarily the upper dot. This can consist of a thermoplastic material, which is scattered onto the lower dot as a powder. After the scattering process, the excess part of the powder (between the dots of the lower layer) is suctioned off again expediently. After the subsequent sintering, the upper dot is (thermally) bonded to the lower dot and can act as an adhesive to the upper dot.
Depending on the intended purpose of the interlining material, a different quantity of dots is printed on and/or the adhesive composition quantity or the geometry of the dot pattern is varied. A typical dot count is for example CP 110 at a coating of 9 g/m2 or CP 52 with a coating quantity of 11 g/m2.
Powder coating and paste printing are also widespread. In the case of paste printing, an aqueous dispersion of thermoplastic polymers, usually in particle form with a particle size <80 μm, thickeners and flow promoting agents is produced and then printed as a paste usually in the form of dots onto the carrier ply by means of a rotary screen printing method. Subsequently, the printed carrier ply is subjected expediently to a drying process.
It is known that many different kinds of hot-melt adhesives can be used as adhesive media for heat bonding for interlining and lining materials.
Hot-melt adhesives, also hot glues, or hot melts, have been known for a long time. Generally, they are understood to be essentially solvent-free products, which are applied in a molten state onto an adhesive surface, set quickly when they cool down and therefore rapidly establish strength. Normally, thermoplastic polymers such as polyamides (PA), copolyamides, polyester (PES), copolyester, ethyl vinyl acetate (EVA) and its copolymers (EVAC), polyethylene (PE), polypropylene (PP), amorphous polyalpha olefins (APAO), polyurethanes (PU), etc. are used as hot-melt adhesives.
In principle, the adhesive effect of the hot-melt adhesives is based on them being able to be reversibly fused as thermoplastic polymers, and as liquid melts they are capable, due to their reduced viscosity resulting from the melting process, of wetting the surface to be bonded and as a result forming an adhesion thereto. As a consequence of the subsequent cooling, the hot-melt adhesive sets again to form a solid which has a high cohesion and in this manner generates the connection to the adhesive surface. After the bonding has taken place, the viscoelastic polymers ensure that the adhesion remains intact even after the cooling process with its changes in volume and the associated build-up of mechanical tensions. The cohesion built up transmits the bonding strength between the substrates.
Because of the different molecular structures of the polymers, their physical and chemical properties such as melting point, viscosity and stability against solvents such as detergent suds and chemical cleaning agents differ from one another. These factors play a decisive role in the selection of the polymer for the field of application of the interlining.
For example, for the field of shirt interlining, which must withstand washing conditions up to 95° C., typically high density polyethylene (hereinafter referred to as “HDPE”) is used as the hot melt adhesive. This polymer has a high melt range, for example from about 130° C., and a low MFI value (melt index or melt-flow index) of 2-20 g/10 minutes (190° C./2.16 kg load). The disadvantage of this is that, as a result of the high melt range and the high viscosity (corresponding to a low MFI value) of the polymer, fusing temperatures greater than 140° C. are necessary. In the drying processes, for example in the tunnel finisher, blistering and delamination of the bonded layers occur. The high mechanical load resulting from the rapidly circulating hot air and the steam supply are extremely demanding on the applied hot-melt adhesive coating. In addition, very large quantities of the HDPE are required to achieve an adequate adhesive effect.
In particular, for use in highly wash resistant applications that are to be dried in demanding conditions, the hot-melt polymers available on the market nowadays are not sufficiently suitable.
Copolyamides, copolyester and low density polyethylene (LDPE) in the melt range from 100-125° C. with MFI values 2-70 g/10 minutes (140° C./2.16 kg load) do not result in acceptable separating force values after multiple care treatments.
A textile fabric with a coating made from two layers of thermoplastic hot-melt adhesives of different compositions lying one on top of the other is known from DE 10 2005 06 470 A1, the second hot-melt adhesive applied to the first hot-melt adhesive having a melting point >135° C. and a melt flow index (MFI) value of 50 to 250 g/10 minutes (190° C./2.16 kg). In the examples, a polyurethane powder with a melt range of 145-155° C. and a polypropylene with a melting point of 160° C. is described as the scatter powder for the upper dot. A disadvantage of the use of hot-melt adhesives with such a high melting point as the upper dot is that the presses used for fusing need to be heated to a very high temperature. For example, a hot-melt adhesive with a melting point of 145° C. is fused at above 165° C. This means that the use of conventional fusing presses, which are designed for fusing temperatures in the range of 120-140° C., is only possible with difficulty. Added to this is that many face materials are too sensitive to be able to be coated at such high fusing temperatures.